#include<stdio.h>

int Fibonacci(int n){
	
	int arr[50]={0,1,1};
	for (int i=3;i<50;i++){
		arr[i]=arr[i-1] + arr[i-2];
	}
	return arr[n];
}

int main(){

	int n;
	scanf("%d",&n);
	
	printf("%d",Fibonacci(n));

	return 0;
}
